Smoke detector for event classification and methods of making and using same

ABSTRACT

Various arrangements for operating a hazard detector are presented. A smoke concentration may be measured using a sensor of the hazard detector. A carbon dioxide concentration may be measured using a carbon dioxide sensor of the hazard detector. The measured smoke concentration may be analyzed in combination with the measured carbon dioxide concentration to determine whether a heads-up alert or warning alarm is to be output. The heads-up alert or the warning alarm may be output based on analyzing the measured smoke concentration in combination with the measured carbon dioxide concentration.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/113,729, filed Aug. 27, 2018, which is a continuation of U.S. patentapplication Ser. No. 15/623,092, filed Jun. 14, 2017, the entiredisclosure of which is incorporated by reference herein for allpurposes.

BACKGROUND

Photoelectric smoke detectors in residential and commercial buildingsinclude a smoke chamber, a light source, a carbon monoxide sensor, and aphotodetector. When smoke from an object enters the smoke chamber, itaffects the photodetector output, which is used to determine aconcentration of smoke in the chamber. The smoke concentration isevaluated together with the carbon monoxide concentration to determineif the smoke is associated with an emergency event or a non-emergencyevent. If the event is an emergency event, the smoke detector generatesa warning alarm. Evaluation of the smoke concentration together with thecarbon monoxide concentration does not allow for an emergency event tobe distinguished from a non-emergency event in all cases.

SUMMARY OF THE EMBODIMENTS

In an embodiment, a method of operating a smoke detector having anilluminator and a light sensor includes the step of measuring a voltagesignal in response to an electromagnetic signal emitted by theilluminator. The method includes determining a smoke concentration usingthe voltage signal, and calculating a rate of increase of smoke. Themethod comprises using the rate of increase of smoke to determine anadjusted smoke concentration, and the step of comparing the adjustedsmoke concentration to a threshold. The method includes generating awarning alarm in response to a finding that the adjusted smokeconcentration exceeds the threshold.

In another embodiment, a smoke detector comprises an illuminatorconfigured to emit an electromagnetic signal, and a light sensorconfigured to generate a voltage signal in response to theelectromagnetic signal. The smoke detector has a carbon monoxide sensor,and a memory storing computer-readable instructions. The smoke detectorincludes a processor configured to execute the instructions to: (a)determine a smoke concentration; (b) calculate a rate of increase ofsmoke based upon a determination that the smoke concentration is in anambiguous zone; (c) determine an adjusted smoke concentration using thesmoke concentration and the rate of increase of smoke; and (d) generatean alarm based on a comparison of the adjusted smoke concentration to athreshold.

In yet another embodiment, a method of operating a smoke detectorcomprising an illuminator, a light sensor, and a carbon monoxide sensorincludes the step of measuring a voltage signal in response to anelectromagnetic signal emitted by the illuminator. The method comprisesthe step of determining a smoke concentration using the voltage signal,and the step of determining a carbon monoxide concentration using thecarbon monoxide sensor. The method includes comparing the smokeconcentration and the carbon monoxide concentration to a warning zonecriteria, and the step of calculating a rate of increase of at least oneof smoke and carbon dioxide based on a determination that the warningzone criteria is unmet. The method comprises generating an alarm inresponse to a determination of a warning condition.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a schematic diagram of a smoke detector, in an embodiment.

FIG. 2 is a schematic diagram of a smoke detector, which is a moredetailed example of the smoke detector of FIG. 1.

FIG. 3 is a schematic diagram illustrating a primary evaluator of thesmoke detector of FIG. 2.

FIG. 4A is a schematic diagram illustrating a warning zone associatedwith the smoke detector of FIG. 2.

FIG. 4B is a schematic diagram illustrating a heads-up zone associatedwith the smoke detector of FIG. 2.

FIG. 5 is a schematic diagram illustrating an alarm generator of thesmoke detector of FIG. 2.

FIG. 6 is a schematic diagram illustrating an ambiguous zone associatedwith the smoke detector of FIG. 2.

FIG. 7 is a schematic diagram illustrating a secondary evaluator of thesmoke detector of FIG. 2.

FIGS. 8A-8B are flowcharts illustrating a method of using the smokedetector of FIG. 2 to distinguish between a warning condition and aheads-up condition.

FIG. 9 is a schematic diagram of a smoke detector, in anotherembodiment.

FIG. 10 is a schematic diagram of a smoke detector, which is a moredetailed example of the smoke detector of FIG. 9.

FIG. 11 is a schematic diagram illustrating a secondary evaluator of thesmoke detector of FIG. 10.

FIG. 12 is a schematic diagram illustrating the rate of increase ofsmoke and carbon dioxide in a heads-up event and an alarm event.

DETAILED DESCRIPTION OF THE EMBODIMENTS

FIG. 1 is a schematic diagram of an example photoelectric lightscattering smoke detector 100 in a room 148 that includes smoke 150.Smoke detector 100 includes a smoke chamber 102, an illuminator 108, acarbon monoxide sensor 120, and a light sensor 130. Illuminator 108 mayinclude one or more light sources 110, which may be a light-emittingdiode (LED), laser diode, or other light source known in the art. Lightsensor 130 may include one or more photodetectors.

Illuminator 108 emits light 112, which includes light portions 112A and112C. Light portion 112A propagates towards the smoke chamber 102 andlight portion 112C propagates towards the light sensor 130. Light sensor130 produces an output voltage 140 in response to detecting lightportion 112C. In a “clean-air” condition, when smoke chamber 102contains no smoke, light sensor 130 detects only light portion 112C andproduces a corresponding clean-air current and associated clean-airvoltage 114. While in that state, the output voltage 140 (which is thusat a clean air voltage level) can be thought of as being in a clean aircondition. However, when smoke 150 is in smoke chamber 102, smoke 150scatters part of light portion 112A as scattered light 112S toward lightsensor 130, which increases output voltage 140. In the clean-air state,when smoke chamber 102 contains no smoke, light portion 112A does notreach light sensor 130.

It is envisioned that the spatial arrangement of smoke chamber 102,illuminator 108, and light sensor 130 may differ from the arrangementillustrated in FIG. 1. Without departing from the scope hereof, smokedetector 100 may be a photoelectric light obscuration smoke detector,such that output voltage 140 falls below clean-air voltage 114 whensmoke 150 is in smoke chamber 102.

FIG. 2 is a schematic diagram of a smoke detector 200, which is anexample of smoke detector 100. Smoke detector 200 may effectuate smokedetection via at least one of photoelectric light scattering andphotoelectric light obscuration. Smoke detector 200 includes illuminator208, smoke chamber 102, a light sensor 230, carbon monoxide sensor 120,and an event monitor 240.

Illuminator 208 is an example of illuminator 108 and includes a firstlight source 210. Light sensor 230 is an example of light sensor 130 andincludes a first photodetector 231. Illuminator 208 may include a secondlight source 220 and light sensor 230 may include a second photodetector232. Light sources 210 and 220 are each an example of light source 110.In some embodiments, the number of light source(s) and photodetector(s)in the illuminator 208 and light sensor 230, respectively, may bedifferent (e.g., the illuminator 208 may have two light sources and thelight sensor 230 may have a solitary photodetector).

The size of particles constituting smoke 150 depends on its source,e.g., on the type of process that produces smoke 150. Illuminator 208may be configured to emit more than one wavelength of light into smokechamber 102, which enables detection of, and differentiation of, typesof smoke that differ in particle size. In an example mode of operation,first light source 210 emits a first optical signal 212 having a firstcenter wavelength λ₁. Illuminator 208, e.g., via second light source220, emits a second optical signal 222 having a second center wavelengthλ₂.

In embodiments, first center wavelength λ₁ exceeds the second centerwavelength λ₂. For example, light source 210 emits near-infrared(near-IR) light and light source 220 emits blue light such that λ₁ isbetween 0.66 μm and 1.0 μm and λ₂ is between 0.40 μm and 0.48 μm. Atleast one of first center wavelength λ₁ and second center wavelength λ₂may be outside the optical portion of the electromagnetic spectrumwithout departing from the scope hereof. For example, second centerwavelength λ₂ may be shorter than 0.40 μm and first center wavelength λ₁may exceed 1.0 μm.

In embodiments where the smoke detector 200 includes, in addition to thefirst light source 210 and the first photodetector 231, the second lightsource 220 and the second photodetector 232, the first photodetector 231is configured to detect first center wavelength λ₁ and the secondphotodetector 232 is configured to detect second center wavelength λ₂.For example, first photodetector 231 includes a bandpass filter thattransmits first center wavelength λ₁ and blocks second center wavelengthλ₂, while second photodetector 232 includes a bandpass filter thattransmits second center wavelength λ₂ and blocks first center wavelengthλ₁. Photodetectors 231 and 232 may have spectral response curvesoptimized for first center wavelength λ₁ and second center wavelengthλ₂, respectively.

Light sensor 230, specifically the first photodetector 231 thereof, isconfigured to produce first photodetector voltage 214 in response to thefirst optical signal 212. The amplitude of the first photodetectorvoltage 214 is proportional to, or otherwise corresponds to, the firstoptical signal 212. The second photodetector 232 of the light sensor 230is configured to produce second photodetector voltage 224 in response tosecond optical signal 222. The amplitude of the second photodetectorvoltage 224 is proportional to, or otherwise corresponds to, the secondoptical signal 222. The first photodetector voltage 214 and the secondphotodetector voltage 224 may be sampled periodically by the eventmonitor 240 to ascertain a concentration of smoke in the chamber 102.

Event monitor 240 is a type of computer. In embodiments, event monitor240 includes a processor 250 and a memory 260, which are communicativelycoupled. Memory 260 may be transitory and/or non-transitory and mayrepresent one or both of volatile memory (e.g., SRAM, DRAM,computational RAM, other volatile memory, or any combination thereof)and non-volatile memory (e.g., FLASH, ROM, magnetic media, opticalmedia, other non-volatile memory, or any combination thereof). Theprocessor 250 represents one or more digital processors. The processor250 may be a microprocessor, and in embodiments, part or all of memory260 may be integrated into processor 250. In some embodiments, theprocessor 250 may be configured through particularly configuredhardware, such as an application specific integrated circuit (ASIC),field-programmable gate array (FPGA), etc., and/or through execution ofsoftware to perform functions in accordance with the disclosure herein.

The event monitor 240, in the memory 260, may store clean air voltage(s)203, photodetector voltage(s) 213, carbon monoxide concentration 160,warning zone criteria 290, heads-up zone criteria 291, threshold(s) 292,and time constant(s) 294. The clean air voltage(s) 203 may include afirst clean air voltage 205 and a second clean air voltage 207, thephotodetector voltage(s) 213 may include the first voltage 214 and thesecond voltage 224, the warning zone criteria 290 may include a firstwarning zone criteria 290A and a second warning zone criteria 290B, theheads-up zone criteria 291 may include a first heads-up zone criteria291A and a second heads-up zone criteria 291B, the threshold(s) 292 mayinclude a first threshold 292A and a second threshold 292B, and the timeconstant(s) 294 may include a first time constant 294A and a second timeconstant 294B. The first clean air voltage 205, first photodetectorvoltage 214, first warning zone criteria 290A, first heads-up zonecriteria 291A, first threshold 292A, and first time constant 294A mayeach be associated with the first light source 210 (e.g., with thenear-infrared source). The second clean air voltage 207, secondphotodetector voltage 224, second warning zone criteria 290B, secondheads-up zone criteria 291B, second threshold 292B, and second timeconstant 294B may each be associated with the second light source 220(e.g., with the blue light source). The discussion below details theoperation of the event monitor 240 with respect to the first voltage 214associated with the first light source 210. The artisan, however, willunderstand that the operation of the event monitor 240 with respect tothe second voltage 224 associated with the second light source 220 maybe generally identical, and that the first voltage 214 and the secondvoltage 224 may, in embodiments, be evaluated by the event monitor 240in parallel.

In embodiments, smoke detector 200 may include a network interface 202that communicatively couples the event monitor 240 to remote data source204A and, in some embodiments, a computing device 204B. Remote datasource 204A is a server, for example. Remote data source 204A mayprovide event monitor 240 with updated versions of at least one of theclean air voltages 203, warning zone criteria 290, heads-up zonecriteria 291, thresholds 292, and time constants 294. Interface 202 is,for example, a network interface such that remote data source 204A andevent monitor 240 communicate via a wired communication channel, awireless communication channel, or a combination thereof. In anembodiment, remote data source 204A includes at least part of the eventmonitor 240, such that at least part of event monitor 240 is remotelylocated from illuminator 208 and light sensor 230.

As discussed herein, the event monitor 240 may, in embodiments,distinguish between a normal condition (or event), a heads-up condition,and a warning condition. Under normal conditions, there may be no smoke150 in the chamber 102 and the first voltage 214 may be generally equalto the first clean air voltage 205. In each of a heads-up event and awarning event, smoke 150 in the chamber 102 may cause the first voltage214 to exceed the first clean air voltage 205. In embodiments, the eventmonitor 240 may cause a heads-up alert to be generated in response to anidentification of a heads-up event. The event monitor 240 may furthercause a warning (or emergency) alarm to be generated in response to anidentification of a warning event. The heads-up alert, where generatedin response to a heads-up event, may indicate that the smokeconcentration and/or carbon monoxide concentration 160 is non-zero, butis currently below emergency levels. The warning alarm generated inresponse to a warning event may indicate that the smoke concentrationand/or carbon monoxide concentration has reached emergency levels. Theheads-up alert may, for example, be a precursor to the warning alarmand/or indicate a nuisance condition. As one example, where smoke from abroiling burger enters the chamber 102, the event monitor 240 maycategorize such as a heads-up event. Alternately, where smoke from aflaming couch (or another burning object) enters the chamber 102, themonitor 240 may categorize the event as a warning event. In someembodiments, the event monitor 240 may initially categorize an event asa heads-up event, and as the smoke concentration and/or carbon monoxidewithin the smoke chamber 102 continues to increase, categorize the eventas a warning event.

The heads-up alert generated in response to a heads-up event may bemilder than a warning alarm generated in response to a warning event.For example, in an embodiment, the heads-up alert may comprise a gentlebeep accompanied by a yellow light, and the emergency alarm may comprisea loud siren accompanied by a red light. In some embodiments, the eventmonitor 240 may identify a warning event, but the identification of theheads-up event may be omitted; in these embodiments, a cautionarynotification may be generated by the event monitor 240 only upon theidentification of a warning event.

In some embodiments, the event monitor 240 (e.g., an alarm generator 276thereof as discussed below) may communicate the heads-up alert or thewarning alarm (e.g., wirelessly, via the interface 202) to the computingdevice 204B of a user or administrator (e.g., a smart phone of the ownerof the structure where the smoke detector 200 is located and/or to thecomputing device of a third party administrator). The user may beallowed to silence or interrupt the heads-up alert via the computingdevice 204B (e.g., the smoke detector 100 may have associated therewitha mobile application installed on the computing device 204B, and theuser may depress a button on an interface of the application to silenceor interrupt the heads-up alert). A warning alarm, on the other hand,may not be so readily silenced and may require additional steps to beturned off.

The smoke detector 200 may be communicatively coupled via the interface202 to another smoke detector or smoke detectors (e.g., the smokedetector 200 in room 148 of a house may be in data communication withthe smoke detector in another room of that house); in these embodiments,when the event monitor 240 of one smoke detector 200 generates aheads-up alert or a warning alarm, the event monitors 240 of other smokedetectors in communication therewith may automatically generate aheads-up alert or warning alarm.

The event monitor 240 may identify an event as one of a normal event, aheads-up event, and a warning event using the software 270. The software270 may be stored in a transitory or non-transitory portion of thememory 260. In an embodiment, the software 270 includes a primaryevaluator 272, a companion (or secondary) evaluator 274, and an alarmgenerator 276. Each of the primary evaluator 272, secondary evaluator274, and alarm generator 276 may include or have associated therewithmachine readable instructions to allow the event monitor 240 to functionas described herein.

The primary evaluator 272 may utilize the first photodetector voltage214, the first clean air voltage 205, and the carbon monoxideconcentration 160 to determine if the event is one of a normal event, aheads-up event, and a warning event. Where the primary evaluator 272 isunable to identify the event as one of a normal event, a heads-up event,and a warning event, the event may be categorized as an ambiguous event.When an event is categorized by the primary evaluator 272 as anambiguous event, the event monitor 240 may call the secondary evaluator274 to evaluate the ambiguous event and resolve the ambiguity. Thesecondary evaluator 274 may determine whether the ambiguous event is aheads-up event or a warning event. In an embodiment, the secondaryevaluator 274 may determine and evaluate the rate of increase of smokein the chamber 102 to identify the event as one of a heads-up event anda warning event.

FIG. 3 shows the primary evaluator 272 in more detail. The primaryevaluator 272 may include a converter 302, an assessor 308, and aprimary characterizer 312. The assessor 308 may initially compare thefirst voltage 214 to the first clean air voltage 205. Where the firstvoltage 214 is generally equal to the first clean air voltage 205, theprimary evaluator 272 may determine that the smoke chamber 102 does notcontain an appreciable quantity of smoke. The primary characterizer 312may therefore identify the event as a normal event (i.e., the primaryevaluator 272 may determine that the smoke detector 200 is operatingunder normal (e.g., clean air) conditions). Alternately, if the firstvoltage 214 is greater than the first clean air voltage 205, the primaryevaluator 272 may evaluate the first voltage 214 to determine if theevent is a heads-up event or a warning event.

The value of the first voltage 214 may relate (e.g., be proportional orotherwise correspond) to the concentration of the smoke 150 in thechamber 102. As is known, the converter 302 may convert the firstvoltage 214 (V) to smoke concentration 304 (dB/m), e.g., by multiplyingthe first voltage 214 with a predefined gain. The assessor 308 may thencompare the smoke concentration 304, and in embodiments, each of thesmoke concentration 304 and the carbon monoxide concentration 160, withthe first warning zone criteria 290A to determine if the event is awarning event. If the first warning zone criteria 290A is met, theprimary characterizer 312 may categorize the event as a warning event.

FIG. 4A schematically illustrates the warning zone 404, in anembodiment. An event may be categorized by the primary characterizer 312as a warning event if the assessor 308 determines that the event fallsin the warning zone 404 (i.e., meets the warning zone criteria 290A). Inthe illustrated embodiment, the warning zone criteria 290A may includethe following: (a) smoke concentration 304 is greater than or equal to0.66 dB/m; or (b) smoke concentration 304 is greater than or equal to0.28 dB/m, and the carbon monoxide concentration 160, as determined bythe carbon monoxide sensor 120, is greater than 10 parts per million. Ifthe assessor 308 determines that either of warning zone criteria (a) or(b) is met, the primary characterizer 312 may categorize the event as awarning event. The alarm generator 276 (FIGS. 2 and 5) may generate awarning alarm 504 in response to apprise the user of a warningcondition. For example, the alarm generator 276 may generate a warningalarm 504 where the smoke concentration 304 is 1.2 dB/m. Similarly, forexample, the alarm generator 276 may generate a warning alarm 504 wherethe smoke concentration 304 is 0.5 dB/m and the carbon monoxideconcentration 160 is 13 parts per million.

If the warning zone criteria 290A is not met, the assessor 308 maycompare the smoke concentration 304 to the first heads-up zone criteria290A. FIG. 4B schematically illustrates the heads-up zone 402, in anembodiment. An event may be categorized by the primary characterizer 312as a heads-up event if the assessor 308 determines that the event fallsin the heads-up zone 402 (i.e., meets the heads-up zone criteria 291A).In the illustrated embodiment, the heads-up zone criteria 291A mayinclude a lower limit and an upper limit of smoke concentration 304. Forexample, as shown in FIG. 4B, the current smoke concentration 304 may bein the heads-up zone 402 if the smoke concentration 304 is greater thanor equal to 0.15 dB/m and is less than 0.28 dB/m. If the assessor 308determines that the smoke concentration 304 is in the heads-up zone 402,the primary characterizer 312 may categorize the event as a heads-upevent, and the alarm generator 276 may generate a heads-up alert 502 inresponse. For example, the alarm generator 276 may generate a heads-upalert 502 where the smoke concentration 304 is 0.21 dB/m.

The current smoke concentration 304 and carbon monoxide concentration160 alone may not allow for the identification of all events as one of aheads-up event and a warning event. More specifically, events fallinginto an ambiguous zone 606 (FIG. 6) may meet neither the warning zonecriteria 290A nor the heads-up zone criteria 291A. If the primaryevaluator 272 is unable to characterize the event as one of a normalevent, a warning event, or a heads-up event, the event may becharacterized by the primary characterizer 312 as an ambiguous event.The event monitor 240 may then call the secondary evaluator 274 toresolve the ambiguity. For example, the event monitor 240 may call thesecondary evaluator 274 where the smoke concentration 304 is 0.42 dB/mand the carbon monoxide concentration 160 is 5 parts per million.

The secondary evaluator 274, shown in more detail in FIG. 7, may includea rate of increase calculator 702, an adjuster 704, a comparator 706,and a secondary characterizer 708. The secondary evaluator 274 maydetermine a rate of increase of smoke 150 in the chamber 102 during atime period, as it has been found that the smoke concentration 304 in awarning event increases at a greater rate as compared to smokeconcentration 304 in a heads-up event. For example, during a given timeperiod (e.g., sixty seconds), smoke generated from a flaming couch mayincrease at a greater rate as compared to smoke generated from abroiling burger. The secondary evaluator 274 may use the rate ofincrease of smoke to determine whether an event falling into theambiguous zone 606 is a warning event or a heads-up event.

In an embodiment, the rate of increase calculator 702 of the secondaryevaluator 274 may initially determine the average rate of increase ofsmoke during a time period (e.g., during sixty seconds, or during adifferent length of time). For example, the smoke rate of increasecalculator 702 may calculate the average smoke rate of increase 702A(dB/m/s) as follows:Average smoke rate of increase 702A=[Smoke concentration 304 (t=t_(o))−Smoke concentration 304 (t=t _(o) −Δt)]/Δt  (Eq. 1)Where:

t_(o)=current sample time; and

Δt=time between samples (e.g., 60 seconds or a different length of timebetween samples).

Once the rate of rise calculator 702 determines the average smoke rateof increase 702A during the time period (e.g., 60 seconds), the adjuster704 may use same and the predefined first time constant 294A todetermine an adjusted smoke concentration 304. In an embodiment, theadjuster 704 may determine the adjusted smoke concentration 304 (dB/m)as follows:Adjusted smoke concentration 304′=Smoke concentration 304 (t=t_(o))+Average smoke rate of increase 702A*time constant 294A  (Eq. 2)

Finally, the comparator 706 may compare the adjusted smoke concentration304′ to the first threshold 292A (FIG. 2). If the adjusted smokeconcentration 304′ is greater than the threshold 292A, which mayindicate a relatively rapid rate of increase of smoke 150 in the chamber102, the secondary characterizer 708 may characterize the event as awarning event. Alternately, if the adjusted smoke concentration 304′ isless than or equal to the first threshold 292A, which may indicate arelatively slow rate of rise of smoke 150 in the chamber 102, thesecondary characterizer 708 may characterize the event as a heads-upevent. The alarm generator 276 may generate a warning alarm 504 if theevent is characterized by the secondary characterizer 708 as a warningevent; alternately, the alarm generator 276 may generate a heads-upalert 502 if the event if categorized by the secondary characterizer 708as a heads-up event. In this way, thus, when smoke concentration 304 andthe carbon monoxide concentration 160 alone do not allow for an event tobe unambiguously categorized as one of a heads-up event and a warningevent, the event monitor 240 may further utilize the average rate ofincrease of smoke 702A to resolve the ambiguity. In essence, the alarmgenerator 276 of the smoke detector 200 may generate a warning alarm 504when any of the following conditions (i)-(iii) are met:

(i) Smoke concentration 304≥0.66 dB/m;

(ii) Smoke concentration 304≥0.28 dB/m and CO concentration 160>10 ppm;or

(iii) Smoke conc. 304≥0.28 dB/m and Adjusted smoke conc. 304′>firstthreshold 292A

As discussed above, the adjusted smoke concentration 304′ may be derivedusing the smoke concentration 304, the average smoke rate of rise 702,and the first time constant 294A. As also discussed above, inembodiments, the event monitor 240 may evaluate the event undercondition (iii) only after it is determined that the event does not meeteither of conditions (i) and (ii).

In an embodiment, the value of the first threshold 292A may be 0.618dB/m, and the value of the first time constant 294A may be 671.51seconds, as it has been found that these numerical values for the firstthreshold 292A and the first time constant 294A may consistently allowfor an event in the ambiguous zone 606 to be correctly identified as oneof a warning event and a heads-up event. Of course, in otherembodiments, and depending on the configuration of the particular smokedetector, different values for the thresholds 292 and the time constants294 may be used (e.g., may be communicated to the event monitor 240 overthe interface 202). As noted above, in embodiments, the smoke alarmgenerator 276 may only generate a cautionary notification when an eventis categorized as a warning event (i.e., the smoke detector 200 may notexpressly apprise the user of a heads-up event or a normal event).

FIG. 8 illustrates a method 800 of using the smoke detector 200 toidentify an event as one of a normal event, a heads-up event, and awarning event. At step 802, the primary evaluator 272, e.g., theassessor 308 thereof, may compare the first voltage 214 to the firstclean air voltage 205. If the first voltage 214 is generally equal tothe first clean air voltage 205 at step 804, the primary evaluator 272may determine that the event is a normal event (e.g., the smoke detector200 is operating under clean-air conditions). The primary characterizer312 may therefore characterize the event as a normal event at step 806.If, on the other hand, the assessor 308 determines at step 804 that thefirst photodetector voltage 214 is greater than (or, in someembodiments, less than) the first clean air voltage 205, the converter302 may, at step 810, convert the first photodetector voltage 214 tosmoke concentration 304.

At step 812, the assessor 308 may compare the smoke concentration 304and the carbon monoxide concentration 160 to the first warning zonecriteria 290A. If the assessor 308 determines at step 814 that the firstwarning zone criteria 290A is met (e.g., the smoke concentration 304 isgreater than or equal to 0.66 dB/m, or the smoke concentration 304 isgreater than or equal to 0.28 dB/m and the carbon monoxide concentration160 is greater than 10 ppm), the primary characterizer 312 may at step816 characterize the event as a warning event. At step 818, based uponthe identification of the event as a warning event, the alarm generator276 may generate warning alarm 504.

If the assessor 308 determines at step 814 that the first warning zonecriteria 290A is not met, the assessor 308 may at step 818 compare thesmoke concentration 304 to the first heads-up zone criteria 291A. If theassessor 308 determines that the heads-up zone criteria 291A is met(e.g., the smoke concentration 304 is greater than or equal to 0.15 dB/mand is less than 0.28 dB/m), the primary characterizer 312 maycharacterize the event as a heads-up event at step 822. At step 824,based upon the identification of the event as a heads-up event, thealarm generator 276 may generate heads-up alert 502.

If, on the other hand, the assessor 308 determines at step 820 that thefirst heads-up zone criteria 291A is not met, the event may be initiallycategorized as an ambiguous event, and the event monitor 240 may callthe secondary evaluator 274 to resolve the ambiguity.

At step 825, the rate of increase calculator 702 of the secondaryevaluator 274 may determine the average smoke rate of increase 702Aduring a predefined time period. For example, as discussed above, therate of increase calculator 702 may determine the average smoke rate ofrise 702A during a given time period using equation 1.

At step 826, the adjuster 704 may determine the adjusted smokeconcentration 304′. For example, the adjuster 704 may determine theadjusted smoke concentration 304′ employing equation 2 above by usingthe current smoke concentration 304, the average smoke rate of increase702A computed previously, and the predefined first time constant 294A.

At step 827, the comparator 706 may compare the adjusted smokeconcentration 304′ to the first threshold 292A. If the adjusted smokeconcentration 304′ is greater than the first threshold 292A at step 828,the secondary characterizer 830 may characterize the event as a warningevent. At step 832, based upon the identification of the event as awarning event, the alarm generator 276 may generate warning alarm 504.Alternately, if at step 828 the adjusted smoke concentration 304′ isless than or equal to the first threshold 292A, the secondarycharacterizer 830 may characterize the event as a heads-up event at step832. The alarm generator 276 may, based upon the identification of theevent as a heads-up event, generate the heads-up alert 502 at step 834.In this way, thus, when smoke concentration 304 and the carbon monoxideconcentration 160 alone do not allow for an event to be unambiguouslycategorized as one of a heads-up event and a warning event, the eventmonitor 240 may further utilize the rate of increase of smoke 702A toresolve the ambiguity.

FIG. 9 shows a smoke detector 900, according to an example embodiment.The smoke detector 900 may be generally identical to the smoke detector100, except as specifically noted and/or shown, or as would be inherent.Those skilled in the art will appreciate that the smoke detector 100(and thus the smoke detector 900) may be modified in various ways, suchas through incorporating all or part of any of the various describedembodiments, for example. For uniformity and brevity, correspondingreference numbers may be used to indicate corresponding parts, thoughwith any noted deviations.

A primary hardware difference between the smoke detector 100 and thesmoke detector 900 may be that, unlike the smoke detector 100, the smokedetector 900 includes a carbon dioxide sensor 920 that determines carbondioxide concentration 960. As discussed above, smoke concentration 304and carbon monoxide concentration 160 alone may not allow for the propercharacterization of an event that falls in the ambiguous zone 606, andthe smoke detectors 100 and 200 may employ the smoke rate of increasecalculator 702 to resolve the ambiguity. The smoke detector 900 may notemploy the smoke rate of increase calculator 702. Rather, where an eventfalls within the ambiguous zone 606, the smoke detector 900 may employthe rate of rise of carbon dioxide (ppm/sec) to determine whether theevent is a warning event. It has been found that akin to smoke 150,which increases more rapidly in a warning event as compared to aheads-up event, the carbon dioxide concentration 960 also increases morerapidly in a warning event as compared to a heads-up event.

FIG. 12 illustrates the rate of rise of smoke and the rate of rise ofcarbon dioxide in each of a heads-up event and a warning event.Specifically, plot 1202 shows the smoke concentration 304 changing overtime for each of a heads-up event (i.e., a broiling burger in thisexample) and a warning event (i.e., flaming polyurethane in thisexample). As can be seen in plot 1202, each of a broiling burger eventand a flaming polyurethane event result in a net increase in the smokeconcentration 304 over a given time period; however, the concentrationof smoke associated with the warning event increases at a faster rate ascompared to the concentration of smoke associated with the heads-upevent.

Plot 1204 illustrates the change in carbon dioxide concentration 960over time for the events illustrated in plot 1202. As is clear, the rateof increase of carbon dioxide is greater for the warning event ascompared to the heads-up event. The smoke detector 900 may use thistrait to distinguish a heads-up event from a warning event.

FIG. 10 is a schematic diagram of a smoke detector 1000, which is anexample of smoke detector 900. The event monitor 1040 thereof has memory1060 which, like memory 260, stores clean air voltage(s) 203,photodetector voltage(s) 213, carbon monoxide concentration 160, warningzone criteria 290, and heads-up zone criteria 291. The memory 1060 mayfurther store the carbon dioxide concentration 960 and carbon dioxiderate threshold 1010.

The event monitor 1040 may have the primary evaluator 272, which may usethe smoke concentration 304 and/or the carbon monoxide concentration 160to determine if an event is one of a normal event, a heads-up event, anda warning event, as discussed above for smoke detector 200. Where theevent falls in the ambiguous zone 606, secondary evaluator 1074 mayevaluate the rate of increase of carbon dioxide concentration 960 over agiven length of time to determine if the rate of increase of carbondioxide (in ppm/sec) exceeds the carbon dioxide rate threshold 1010.

FIG. 11 shows the secondary evaluator 1074 in additional detail. Thesecondary evaluator 1074 may have a rate of increase calculator 1102,which may calculate the rate of increase of carbon dioxide 1102A in thechamber 102 over a given time period (e.g., over one second, fiveseconds, ten seconds, or a different time period). The comparator 1106may then compare the carbon dioxide rate of increase 1102A with thecarbon dioxide rate threshold 1010. If the carbon dioxide rate ofincrease 1102A is greater than or equal to the carbon dioxide ratethreshold 1010, the secondary characterizer 1108 may characterize theevent as a warning event, and the alarm generator 276 may generate awarning alarm 504 in response. Alternately, if the rate of increase ofcarbon dioxide 1102A is below the carbon dioxide rate threshold 1010,the secondary characterizer 1108 may characterize the event as aheads-up event, and the alarm generator 276 may, in embodiments,generate a heads-up alert 502 in response. As discussed above for smokedetector 200, in embodiments, the smoke detector 1000 may identify awarning event, but the identification of the heads-up event may beomitted; in these embodiments, a cautionary notification may begenerated by the event monitor 1040 only upon the identification of awarning event. In essence, the smoke detector 1000 may generate awarning alarm when any of the following conditions (iv)-(vi) are met:

(iv) Smoke concentration 304≥0.66 dB/m;

(v) Smoke concentration 304≥0.28 dB/m and CO concentration 160>10 ppm;or

(vi) Smoke conc. 304≥0.28 dB/m and CO₂ rate of increase 1102A>CO₂ ratethreshold 1010.

It will be appreciated that conditions (iv) and (v) are the same ascondition (i) and (ii), respectively, discussed above for the smokedetector 200. In embodiments, the event monitor 1040 may evaluate theevent under condition (vi) only after it is determined that the eventdoes not meet either of conditions (iv) and (v). It is envisioned thatin some embodiments, to reduce false positives, the smoke rate of riseand the carbon dioxide rate of increase will be evaluated in the smokedetector in parallel.

In an embodiment, the numerical value for the CO₂ rate threshold 1010may be about 11 ppm/sec. In some embodiments, to reduce false positives,condition (vi) may be considered met only where each of a plurality ofconsecutive readings (e.g., five consecutive readings) of the CO₂ sensor920 indicate that the CO₂ rate of increase 1102A is greater than orequal to the carbon dioxide rate threshold 1010.

Thus, as has been described, the smoke detectors 200 and 1000 mayrespectively evaluate the rate of increase of smoke and the rate of riseof carbon dioxide to consistently identify a warning event. Changes maybe made in the above methods and systems without departing from thescope hereof. It should thus be noted that the matter contained in theabove description or shown in the accompanying drawings should beinterpreted as illustrative and not in a limiting sense. The followingclaims are intended to cover all generic and specific features describedherein, as well as all statements of the scope of the present method andsystem, which, as a matter of language, might be said to falltherebetween.

What is claimed is:
 1. A method for operating a hazard detector, themethod comprising: measuring a smoke concentration using a sensor of thehazard detector; measuring a carbon dioxide concentration using a carbondioxide sensor of the hazard detector; determining a rate of increase ofthe measured carbon dioxide concentration; analyzing the measured smokeconcentration in combination with the rate of increase of the measuredcarbon dioxide concentration to determine that a heads-up alert is to beoutput instead of a warning alarm, wherein: analyzing the measured smokeconcentration in combination with the measured carbon dioxideconcentration comprises comparing the measured smoke concentration to afirst threshold and comparing the measured carbon dioxide concentrationto a second threshold; and the heads-up alert indicates a presence of ahazard, but that the hazard is below emergency levels; and the warningalarm indicates the hazard has reached emergency levels; and outputtingthe heads-up alert based on analyzing the measured smoke concentrationin combination with the measured carbon dioxide concentration.
 2. Themethod for operating the hazard detector of claim 1, further comprising:determining a rate of increase of carbon dioxide concentration.
 3. Themethod for operating the hazard detector of claim 2, wherein analyzingthe measured smoke concentration in combination with the measured carbondioxide concentration comprises analyzing the rate of increase of carbondioxide concentration.
 4. The method for operating the hazard detectorof claim 3, wherein analyzing the rate of increase of carbon dioxideconcentration comprises comparing the rate of increase of carbon dioxideto a carbon dioxide rate threshold.
 5. The method for operating thehazard detector of claim 1, wherein measuring the smoke concentrationcomprises measuring a voltage output by a light sensor of the hazarddetector.
 6. The method for operating the hazard detector of claim 1,further comprising: measuring a carbon monoxide concentration, whereinanalyzing the measured smoke concentration in combination with themeasured carbon dioxide concentration further comprises analyzing themeasured carbon monoxide concentration.
 7. A hazard detector,comprising: a carbon dioxide sensor; a smoke sensor; a memory storingprocessor-readable instructions; and one or more processors configuredto execute the processor-readable instructions that cause the one ormore processors to: determine a smoke concentration using a firstmeasurement by the smoke sensor; determine a carbon dioxideconcentration using a second measurement by the carbon dioxide sensor;determine a rate of increase of the measured carbon dioxideconcentration; analyze the measured smoke concentration in combinationwith the rate of increase of the measured carbon dioxide concentrationto determine that a heads-up alert is to be output instead of a warningalarm, wherein: the one or more processors being configured to executethe processor-readable instructions that cause the one or moreprocessors to analyze the measured smoke concentration in combinationwith the measured carbon dioxide concentration comprises the one or moreprocessors being configured to compare the measured smoke concentrationto a first threshold and compare the measured carbon dioxideconcentration to a second threshold; and the heads-up alert indicates apresence of a hazard, but that the hazard is below emergency levels; andthe warning alarm indicates the hazard has reached emergency levels; andcause the heads-up alert to be output by the hazard detector based onanalyzing the measured smoke concentration in combination with themeasured carbon dioxide concentration.
 8. The hazard detector of claim7, wherein the processor-readable instructions that cause the one ormore processors to analyze the rate of increase of carbon dioxidecomprises the processor-readable instructions that cause the one or moreprocessors to compare the rate of increase of carbon dioxide to a carbondioxide rate threshold.
 9. The hazard detector of claim 7, furthercomprising: a carbon monoxide sensor, wherein the processor-readableinstructions further cause the one or more processors to: determine acarbon monoxide concentration based on a measurement output by thecarbon monoxide sensor, wherein the processor-readable instructions thatcause the one or more processors to analyze the measured smokeconcentration in combination with the measured carbon dioxideconcentration further comprises analyzing the measured carbon monoxideconcentration.
 10. A non-transitory processor-readable medium configuredto cause one or more processors to: determine a smoke concentrationusing a first measurement from a smoke sensor; determine a carbondioxide concentration using a second measurement from a carbon dioxidesensor; determine a rate of increase of the measured carbon dioxideconcentration; analyze the measured smoke concentration in combinationwith the rate of increase of the measured carbon dioxide concentrationto determine that a heads-up alert is to be output instead of a warningalarm, wherein: the non-transitory processor-readable medium beingconfigured to cause the one or more processors to analyze the measuredsmoke concentration in combination with the measured carbon dioxideconcentration comprises the one or more processors being caused tocompare the measured smoke concentration to a first threshold andcompare the measured carbon dioxide concentration to a second threshold;and the heads-up alert indicates a presence of a hazard, but that thehazard is below emergency levels; and the warning alarm indicates thehazard has reached emergency levels; and cause the heads-up alert to beoutput based on analyzing the measured smoke concentration incombination with the measured carbon dioxide concentration.